The history of Caius is veiled in obscurity. All that we know of him is that he was a very learned ecclesiastical writer, who at the beginning of the third century held a disputation with Proclus in Rome (cf. Bk. VI. chap. 20, below). The accounts of him given by Jerome, Theodoret, and Nicephorus are drawn from Eusebius and furnish us no new data. Photius, however (Bibl. XLVIII.), reports that Caius was said to have been a presbyter of the Roman Church during the episcopates of Victor and Zephyrinus, and to have been elected “Bishop of the Gentiles,” and hence he is commonly spoken of as a presbyter of the Roman Church, though the tradition rests certainly upon a very slender foundation, as Photius lived some six hundred years after Caius, and is the first to mention the fact. Photius also, although with hesitation, ascribes to Caius a work On the Cause of the Universe, and one called The Labyrinth, and another Against the Heresy of Artemon (see below, Bk. V. chap. 28, note 1). The first of these (and by some the last also), is now commonly ascribed to Hippolytus. Though the second may have been written by Caius it is no longer extant, and hence all that we have of his writings are the fragments of the Dialogue with Proclus preserved by Eusebius in this chapter and in Bk. III. chaps. 28, 31. The absence of any notice of the personal activity of so distinguished a writer has led some critics (e.g. Salmon in Smith and Wace, I. p. 386, who refers to Lightfoot, Journal of Philology, I. 98, as holding the same view) to assume the identity of Caius and Hippolytus, supposing that Hippolytus in the Dialogue with Proclus styled himself simply by his prænomen Caius and that thus as the book fell into the hands of strangers the tradition arose of a writer Caius who in reality never had a separate existence. This theory is ingenious, and in many respects plausible, and certainly cannot be disproved (owing chiefly to our lack of knowledge about Caius), and yet in the absence of any proof that Hippolytus actually bore the prænomen Caius it can be regarded as no more than a bare hypothesis. The two are distinguished by Eusebius and by all the writers who mention them. On Caius’ attitude toward the Apocalypse, see Bk. III. chap. 28, note 4; and on his opinion in regard to the authorship of the Epistle to the Hebrews, see Bk. VI. chap. 20, and Bk. III. chap. 3, note 17. The fragments of Caius (including fragments from the Little Labyrinth, mentioned above) are given with annotations in Routh’s Rel. Sacræ, II. 125–158 and in translation (with the addition of the Muratorian Fragment, wrongly ascribed to Caius by its discoverer) in the Ante-Nicene Fathers, V. 599–604. See also the article of Salmon in Smith and Wace, of Harnack, in Herzog (2d ed.), and Schaff’s Ch. Hist. II. p. 775 sqq.